PARUPM: A simulation code for passive auto-catalytic recombiners

Abstract

In the event of a severe accident with core damage in a water-cooled nuclear reactor, combustible gases (H2 and possibly CO) get released into the containment atmosphere. An uncontrolled combustion of a large cloud with a high concentration of combustible gases could lead to a threat to the containment integrity if concentrations within their flammability limits are reached. To mitigate this containment failure risk, many countries have proceeded to install passive auto-catalytic recombiners (PARs) inside containment buildings. These devices represent a passive strategy for controlling combustible gases, since they can convert H2 and CO into H2O and CO2, respectively. In this work, the code PARUPM developed by the Department of Energy Engineering at the UPM is described. This work is part of the AMHYCO project (Euratom 2014–2018, GA No. 945057) aiming at improving experimental knowledge and simulation capabilities for the H2/CO combustion risk management in severe accidents (SAs). Thus, enhancing the available knowledge related to PAR operational performance is one key point of the project. The PARUPM code includes a physicochemical model developed for the simulation of surface chemistry, and heat and species mass transfer between the catalytic sheets and gaseous mixtures of hydrogen, carbon monoxide, air, steam and carbon dioxide. This model involves a simplified Deutschmann reaction scheme for the surface combustion of methane, and the Elenbaas analysis for buoyancy-induced heat transfer between parallel plates. Mass transfer is considered using the heat and mass transfer analogy. By simulating the recombination reactions of H2 and CO inside the catalytic section of the PAR, PARUPM allows studying the effect of CO on transients related to accidents that advance towards the ex-vessel phase. A thorough analysis of the code capabilities by comparing the numerical results with experimental data obtained from the REKO-3 facility has been executed. This analysis allows for establishing the ranges in which the code is validated and to further expands the capabilities of the simulation code which will lead to its coupling with thermal-hydraulic codes in future steps of the project.